Ureteral peristaltic activity begins with the origin of electrical activity at pacemaker sites. These sites are located in the proximal portion of the urinary collecting system. The `atypical' smooth muscle cells at these sites fire `pacemaker' potentials at a frequency higher than the `driven' action potentials recorded from typical smooth muscle cells. In contrast to typical smooth muscle cells, these atypical pacemaker cells have less than 40% of their cellular area occupied by contractile filaments and demonstrate a sparse immunoreactivity for alpha-smooth muscle actin. Expression of c-Kit, a tyrosine kinase receptor, correlates with the onset of organized ureteral peristalsis in the embryo. Capsaicin-sensitive sensory afferents and the endogenous release of tachykinins and prostaglandins are involved in the maintenance of normal ureteral peristalsis.
An alternative model for the measurement of ureteral peristalsis is described using the goat ureter. Ureters from freshly slaughtered goats (Capra aegagous hircus) were collected from a local slaughter house. The peristaltic reflex of these preparations was recorded using a specially designed apparatus. The preparations were mounted so that contractile responses to drugs could be recorded isometrically. Histological studies were undertaken to enable a correlation to be made between the anatomical observations and the functional studies. The spontaneous peristaltic reflex of the goat ureter (7 ± 2 per 2 min) showed a 50% increase in the frequency of contraction (13.66 ± 1.6, P<0.001) after application of histamine at a concentration of between 6.512 μM and 13.024 μM, but was blocked completely by 10.4 μM of pheniramine (P>0.05). The reflex was not blocked by the H2 blocker ranitidine (P<0.001). The effects of acetylcholine were variable. Calcium chloride at 6.8 μM resulted in a tetanic response (P<0.001). Nicorandil showed partial inhibition of spontaneous peristaltic reflex at 189.4 μM and complete inhibition at 473.4 μM (P<0.001). Although acetylcholine did not show any appreciable effect on the isometric contractions at a maximum dose of 275.2 μM, adrenaline increased the frequency of contractions by 8.2 ± 6.5 (P<0.001), while salbutamol and isoprenaline had no effect. The histology revealed a striking resemblance to the human ureter, with a structure that explained the responses obtained. The anatomic, physiologic and histological similarities to the human ureter make it an effective alternative in tropical countries for research on ureteral peristalsis.
The effects of aging on α1-adrenoceptor (α1-AR)-mediated contractile response in endothelium-removed aortic preparations isolated from 5- to 40-week-old (5-, 6-, 8-, 10-, 20-, 40-weeks) mice were studied in the presence of propranolol. The potency of noradrenaline, estimated as its pD2 value, increased with age from 5- to 10-weeks, but decreased thereafter with age from 10- to 40-weeks. However, the affinity of prazosin (pA2 value) did not change with aging. These results suggest that age-related change in noradrenaline potency is not attributable to the change of drug affinity to α1-ARs, but is possibly due to drug affinity-unrelated factors such as change of the reserve of α1-ARs.